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This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science.

Trace Gas Emissions

Since the beginning of the industrial revolution, humans have
transformed about 40 percent of Earth's land surface and have increased
carbon dioxide levels by about 25 percent. Scientists estimate that from
1850 to 1980, between 90 and 120 billion metric tons (90-120 trillion
kilograms) of carbon dioxide were released into the atmosphere from
tropical forest fires. Comparatively, during that same time period, an
estimated 165 billion metric tons of carbon dioxide were added to the
atmosphere by industrial nations through the burning of coal, oil, and
gas. Today, an estimated 5.6 gigatons of carbon are released into the
atmosphere each year due to fossil fuel burning. Burning of tropical
forests contributes another 2.4 gigatons of carbon per year; or, about
30 percent of the total.

Over the last decade, it seems that the regional distribution of biomass
burning has increased worldwide, as well as the length of burning time.
The result is a continuing increase in the release of emission products,
and an increase in the severity of their impact on climate and on the
environment. Scientists estimate that in just a few months the burning that
took place in 1997 in Indonesia released as many greenhouse gases as all
the cars and power plants in Europe emit in an entire year.

After carbon dioxide, the most significant greenhouse gas is methane,
another emission product from biomass burning (about 10 percent
globally). Although methane is about 200 times less abundant than carbon
dioxide in the atmosphere, molecule for molecule methane is 20 times
more effective at trapping heat. Since the beginning of the Industrial
Revolution, methane has doubled in the troposphere. Additionally, its
concentration has been increasing about 1 percent per year, so
scientists are concerned that its relative significance as a greenhouse
gas may dramatically increase in the future, although there are
indications that this increase may have slowed down in the last decade.

Nitrous oxide (N2O) concentrations have been increasing at about 0.3
percent per year for the last several decades. Yet, nitrous oxide has a
lifetime of 150 years in the atmosphere, which contrasts sharply with
the 10-year lifetime of methane. A single nitrous oxide molecule is the
equivalent of 206 carbon dioxide molecules in terms of its greenhouse
gas effect. Biomass burning accounts for about 2-3 percent of the total
amount of tropospheric nitrous oxide. Emissions of nitrous oxides and
methane are further associated with the production of tropospheric
ozone. Unlike "good" ozone in the stratosphere (upper atmosphere) that
acts as a shield to screen out the sun's harmful ultraviolet rays, ozone
in the troposphere is a pollutant that, when breathed, damages lung
tissue and is also harmful to plants.

Greenhouse gasessuch as carbon dioxide, methane, and nitrous oxideare
mostly "transparent" to incoming solar radiation; that is, they rarely
interact with sunlight. However, these gases are very efficient at trapping heat
radiated from the Earth's surface by absorbing and re-emitting it.

There is a wide margin of error in the estimates of biomass burning given abovesignificantly more
error than in our estimates of industrial emissions. The accuracy of
scientist's biomass burning emission estimates must be improved if they
are to better understand, model and predict the impacts of the emissions
on climate change.

Top Left: In addition to the visible plume of smoke and ash, fires release gases such as
carbon dioxided and methane into the atmosphere. The gasses from wildland fires may
play an important part in future global climate change. (Photograph courtesy Yoram Kaufman,
NASA Goddard Space Flight Center)